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typescript.cpu_in_event_loop

Performance High

Detects CPU-intensive operations that block Node.js event loop.

Why It Matters

Blocking event loop:

All requests stalled — Single-threaded Node.js freezes
Timeouts — Other operations time out
Poor scalability — Can’t handle concurrent load

Example

// ❌ Before (blocking event loop)
app.get('/hash', (req, res) => {
  const hash = crypto.pbkdf2Sync(req.body.password, salt, 100000, 64, 'sha512');
  res.json({ hash: hash.toString('hex') });
});

// ✅ After (offload to worker)
import { Worker } from 'worker_threads';

app.get('/hash', async (req, res) => {
  const hash = await runInWorker(req.body.password);
  res.json({ hash });
});

// Or use async version:
app.get('/hash', async (req, res) => {
  const hash = await new Promise((resolve, reject) => {
    crypto.pbkdf2(req.body.password, salt, 100000, 64, 'sha512', (err, key) => {
      if (err) reject(err);
      else resolve(key.toString('hex'));
    });
  });
  res.json({ hash });
});

What Unfault Detects

Sync crypto operations in request handlers
Large JSON.parse/stringify in hot paths
Heavy loops without yielding